This Career Development Award (K01) will provide the candidate with the necessary skills to develop an independent research program focused on integrating genetic methodologies to the candidate's already strong longitudinal modeling skills to explore and clarify the etiology of the interplay between cigarette use and internalizing problems during adolescence. Despite decreases in prevalence of smoking during adolescence in the past two decades, adolescence continues to be the developmental period of greatest risk for cigarette use onset and increase in internalizing problems. Clarifying the complex etiological pathways involved in the co-occurrence between cigarette use and internalizing problems during this vulnerable time requires using multiple methodologies. The overall aim of the current proposal is to test increasingly complex longitudinal models that explore the degree to which the co-occurrence between adolescent cigarette use and internalizing problems are influenced by genetic and environmental factors and to include measured genetic variants. The training plan will be completed at the Virginia Institute for Psychiatric and Behavioral Genetics at Virginia Commonwealth University and is designed to provide the candidate with skills in genetic epidemiology, quantitative genetics, and molecular genetics. The candidate will acquire the knowledge and skills to a) conduct univariate, bivariate, and multivariate genetically informed studies to identify the genetic and environmental risk factors in smoking initiation, progression t heavier smoking, nicotine dependence, and internalizing problems; b) conduct longitudinal genetically informed studies to clarify the causal pathways involved in cigarette use and internalizing problems by exploring the degree to which genetic and environmental factors explain the covariance between the behaviors; and c) conduct genetically informed ecological momentary assessment studies of adolescent twin pairs to explore the causal pathway between these problems behaviors. These skills will be developed through a combination of formal coursework, mentored research projects, and didactic training. The proposed research program involves a combination of analysis of existing longitudinal studies of adolescent twins and an original data collection pilot project. The existing longitudinal studies of adolescent twins inclue the Swedish Twin Study of Child and Adolescent Development, the Minnesota Twin and Family Study, the Virginia Twin Study of Adolescent Behavioral Development, the National Longitudinal Study of Adolescent Health, the GEDI (Genes, Environment, Development Initiative part of NIDA's Genetics Consortium). In the pilot project, the candidate will collect momentary cigarette use and mood data of 16- and 17-year-old adolescent twin pairs recruited from a population-based twin registry comprised of over 50,000 twins. Training activities and results will be used to develop a R01 proposal for a prospective momentary assessment and genotyping study of 14 to 17 year old adolescent twins.